This invention relates to honeycombed structures having thin-walled, open-ended cells, and more particularly, to structures of this type comprising ceramic or similar sinterable materials.
Catalytic reactors which are utilized in emission control devices in automobiles may comprise a ceramic substrate having open-ended cells which extend from one end of the substrate to another where the thin walls forming the open-ended cells are coated with a high surface area, active metal oxide impregnated with a catalytically active substance such as are disclosed in copending application Ser. No. 333,642, filed Feb. 20, 1973 (assigned to the assignee of this application now abandoned). As an alternative, catalytic reactors may comprise honeycombed structures wherein the walls of the open-ended cells comprise a catalytically active substance which is mixed and extruded with ceramic material as disclosed in British patent specification No. 1,142,800 and Belgian Pat. No. 783,126. In structures of this type, hot gases flow through the open-ended cells and reactions are promoted by the catalytically active substance to rid the gases of undesirable pollutants. Similarly, honeycombed structures of this general type are well suited for use as heat exchangers or similar devices subjected to thermal shock conditions.
The foregoing structures which may be utilized in catalytic reactors and heat exchangers may comprise fabricated monoliths such as those disclosed in U.S. Pat. Nos. 3,112,184; 3,444,925 and 3,775,204 or extruded structures such as those described in British patent specification No. 1,142,800, Belgian Pat. No. 783,126 and U.S. Pat. No. 3,790,654. These fabricated and extruded structures result in generally uniform cell walls with a considerable surface area as required for effective use as a catalytic reactor or heat exchanger. It is also desirable that such structures be characterized by a high degree of thermal shock resistance so as to prevent cracking, fracturing or other permanent deformation of the structures during temperature cycling. This thermal shock resistance is particularly important when the structure is to be utilized as a catalytic reactor for an automobile engine which must be started and stopped under all kinds of temperature conditions time and time again without failure of the catalytic reactor.